1. Field of the Invention.
The invention relates to apparatus and methods for handling diving vehicles, and more particularly, to apparatus and methods for lowering and lifting diving bells between the ocean surface and the deck of a vessel.
2. Description of the Prior Art.
Diving bells have been used for years in oceanographic research and related commercial applications. Recently, diving bells have been used in large numbers in the offshore petroleum industry, for example, in the installation and inspection of offshore pipelines.
In the handling of suspended or tethered diving bells it is well known that when a bell is lifted from the water by a hoist cable, waves striking the bell and motions of the marine structure may cause a serious pendulum effect resulting in violent motions of the diving bell. A first step in reducing the pendulum effect is to shorten the length of vertical travel as much as possible. However, the suspension of the diving bell requires a certain length of cable which necessarily results in the danger of a pendulum effect. A handling system dealing with the above-described pendulum problem is described in U.S. Pat. No. 3,518,837 which discloses a stabilizing bar that rides in contact with the top of the diving vessel as it is being lifted upwardly toward a support frame.
It has been found that a primary cause of the dangerous pendulum effect is that the diving bell is ordinarily raised quite slowly, especially during the least few feet of travel. Furthermore, after the bell has been fully raised by the hoist cable, according to prior art practices it has not been stabilized before moving it to a position over the deck of the vessel or marine platform.
One aspect of the present invention is the provision of a handling system whereby the vehicle may be raised rapidly from the water surface to a stabilized frame where it is secured over the water.
Another aspect of the invention is the provision of mating surfaces on the diving bell and the support frame such that the mating surfaces will automatically self-align and lock to stabilize the bell.